Efficient snapshot management in a large capacity disk environment

ABSTRACT

A method, computer program product and/or system saves an original logical block in a file system and generates a first heatmap reflecting access operations on the original logical block. After taking of a file system snapshot, and receiving information that the original logical block is going to be revised, a second heatmap is generated, reflecting predicted access operations on the revised logical block. The second heatmap is based, at least in part, on the first heatmap. Selecting a physical storage location for the revised logical block is based on the second heatmap.

BACKGROUND

The present invention relates generally to the field of snapshotmanagement for computer data storage software, and more particularly tosnapshot management for software managing and controlling a largecapacity disk type data storage device such as a shingled magneticrecording/high storage density storage system.

A file system defines rules for naming files and placing them on astorage device for storage and retrieval. File system functionality canbe divided into two components: a user component and a storagecomponent. The user component is responsible for managing files withindirectories, file path traversals and user access to the files. Thestorage component of the file system determines the physical locationswhere files are stored on the storage device.

In conventional storage systems, a file system snapshot is a record ofthe state of a storage device or file system at any given moment intime. The snapshot is a guide for restoring a file, a storage device ora file system in the event, for example, that the storage device fails.Typically, a snapshot is made essentially instantly, and is madeavailable for use by other applications for purposes such as: (i) dataprotection; (ii) data analysis and reporting; and/or (iii) datareplication.

In some snapshot implementations, (including copy-on-write snapshotimplementations, which will be further discussed below), a snapshot is arecord of the state of a file system including the date and time thesnapshot was taken. After a snapshot is taken, if a file, or a portionof the file (herein called a data block, or a block) is to be updated, anew instance of the data block is created and stored at a physicaladdress different from the original data block. The new instance becomesthe active block and the previous instance now becomes an inactiveblock. The file system, while keeping the inactive data block intact,updates its pointers to reference the active data block. To a typicaluser, nothing appears to have changed. The inactive data block(sometimes called the snapshot data), which is no longer accessible tosome software, remains on the storage device and can be re-activated byan operation to restore the file (or even the whole file system) to thestate at which it existed at the time the snapshot was taken. The activedata block is stored on the storage device at a physical address thatmay have a shorter or longer access time relative to the inactive datablock, and, consequently, a user may experience a change in the responsetime of the file system when an access operation involves the updatedfile.

The active data block (sometimes herein variously referred to as the“latest data”, the “live data” or the “primary data”) continues to beavailable to applications without interruption, while the inactive datablock: (i) is used to perform other functions on the data; (ii) enablesimproved application availability; (iii) enables faster recovery fromfailures or service interruptions; (iv) enables easier back upmanagement of large volumes of data; (v) reduces exposure to data loss;(vi) virtually eliminates backup windows; and/or (vii) lowers total costof ownership of a backup solution.

In a conventional storage system with “multi-tier” architecture,different categories of data are respectively stored on different“tiers” of the storage system, typically based on criteria such as:frequency of use; security requirements; data recovery requirements;and/or other access-related criteria. Examples of different storagetiers include: (i) SSD (solid state storage device); (ii) SAS (serialattached SCSI); (iii) nearline SAS, etc. Different tiers basicallyrepresent different classes or qualities of service. The tierclassification can vary based on factors such as speed, cost etc.

On some disk-type storage devices, there is a linear speed ratio betweentracks stored on an outer partition and tracks stored on an innerpartition. The speed ratio typically is close to 5/3 (outer/inner). Forexample, a drive that is capable of 120 MB/sec data transfer speed withrespect to data on the outer tracks might yield only 72 MB/sec datatransfer speed with respect to data stored on the inner tracks.

In some conventional systems, “copy-on-write” (COW) is the underlyingmechanism for disk storage snapshots. In some COW data storage systems,multiple versions (for example, a version corresponding to eachsuccessive instance of a snapshot followed by a write operation) of aninactive data block are retained, and accumulated since the time thedata block first came into existence.

In a large disk environment (for example a shingled magneticrecording/high storage density or SMR storage system), tiered storagecan be implemented wherein data with high access frequency are movedonto outer tracks (which can deliver higher read/write speed), and lowfrequency/archival data are moved onto inner tracks (which deliverscomparatively lower read/write speed).

SUMMARY

According to an aspect of the present invention, there is a method,computer program product and/or system that performs the followingoperations (not necessarily in the following order): (i) saving anoriginal logical block in a file system at a first physical location;(ii) generating a first heatmap reflecting access operations on theoriginal logical block; (iii) taking of a first snapshot with respect toat least a portion of the file system including the original logicalblock; (iv) receiving information that the original logical block isgoing to be revised into a revised logical block; (v) generating asecond heatmap reflecting predicted access operations on the revisedlogical block, with the second heatmap being based at least in part onthe first heatmap; (vi) selecting a second physical storage location forthe revised logical block based at least in part on the second heatmap;and (vii) saving the revised logical block at the second physicalstorage location.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram view of a first embodiment of a systemaccording to the present invention;

FIG. 1B is a block diagram view of a first embodiment of a systemaccording to the present invention;

FIG. 2 is a flowchart showing a first embodiment method performed, atleast in part, by the first embodiment system;

FIG. 3 is a block diagram showing a machine logic (for example,software) portion of the first embodiment system;

FIG. 4 is a table showing information that is helpful in understandingembodiments of the present invention;

FIG. 5 is a flowchart of a first embodiment of a method according to thepresent invention; and

FIG. 6 is a flowchart of a second embodiment of a method according tothe present invention.

DETAILED DESCRIPTION

A method for determining optimal placement of logical blocks in storagesystems of tiered architecture, to efficiently manage high performancetiers in a multi-tier storage architecture (large disk capacityenvironment). Performed at a first write operation after a snapshotcreation, the method is based on heatmaps (access history) of thelogical blocks. A proportion of heatmap information is transferred froman existing logical block to a corresponding new logical block based onpredicted application behavior. The new logical block is placed on inneror outer disk tracks during a first write after snapshot (COW-copy onwrite). Placement of the logical block is based on the heatmapinformation from the old logical block. This Detailed Descriptionsection is divided into the following sub-sections: (i) The Hardware andSoftware Environment; (ii) Example Embodiment; (iii) Further Commentsand/or Embodiments; and (iv) Definitions.

I. The Hardware and Software Environment

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operations to be performed on the computer, otherprogrammable apparatus or other device to produce a computer implementedprocess, such that the instructions which execute on the computer, otherprogrammable apparatus, or other device implement the functions/actsspecified in the flowchart and/or block diagram block or blocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

An embodiment of a possible hardware and software environment forsoftware and/or methods according to the present invention will now bedescribed in detail with reference to the Figures. FIG. 1A is afunctional block diagram illustrating various portions of networkedcomputers system 100, including: server sub-system 102; client computers104 and 106; communication network 114; server computer 200;communication unit 202; processor set 204; input/output (I/O) interfaceset 206; memory device 208; persistent storage device 210; displaydevice 212; external device set 214; random access memory (RAM) devices230; cache memory device 232; and storage management program 300.

FIG. 1B is a functional block diagram illustrating various portions ofexternal device set 214, including: multi-tier file system device 240;first-tier module 241; fast access physical address space 245; originaldata block (also called “original logical block”) 251; second-tiermodule 242; fast access physical address space 246; medium accessphysical address space 247; slow access physical address space 248; andrevised data block 252.

Server sub-system 102 is, in many respects, representative of thevarious computer sub-system(s) in the present invention. Accordingly,several portions of server sub-system 102 will now be discussed in thefollowing paragraphs.

Server sub-system 102 may be a laptop computer, tablet computer, netbookcomputer, personal computer (PC), a desktop computer, a personal digitalassistant (PDA), a smart phone, or any programmable electronic devicecapable of communicating with the client sub-systems via network 114.Storage management program 300 is a collection of machine readableinstructions and/or data that is used to create, manage and controlcertain software functions that will be discussed in detail, below, inthe Example Embodiment sub-section of this Detailed Description section.

Server sub-system 102 is capable of communicating with other computersub-systems via network 114. Network 114 can be, for example, a localarea network (LAN), a wide area network (WAN) such as the Internet, or acombination of the two, and can include wired, wireless, or fiber opticconnections. In general, network 114 can be any combination ofconnections and protocols that will support communications betweenserver and client sub-systems.

Server sub-system 102 is shown as a block diagram with many doublearrows. These double arrows (no separate reference numerals) represent acommunications fabric, which provides communications between variouscomponents of server sub-system 102. This communications fabric can beimplemented with any architecture designed for passing data and/orcontrol information between processors (such as microprocessors,communications and network processors, etc.), system memory, peripheraldevices, and any other hardware components within a system. For example,the communications fabric can be implemented, at least in part, with oneor more buses.

Memory 208 and persistent storage 210 are computer-readable storagemedia. In general, memory 208 can include any suitable volatile ornon-volatile computer-readable storage media. It is further noted that,now and/or in the near future: (i) external device(s) 214 may be able tosupply, some or all, memory for server sub-system 102; and/or (ii)devices external to server sub-system 102 may be able to provide memoryfor server sub-system 102.

Storage management program 300 is stored in persistent storage 210 foraccess and/or execution by one or more of the respective computerprocessors 204, usually through one or more memories of memory 208.Persistent storage 210: (i) is at least more persistent than a signal intransit; (ii) stores the program (including its soft logic and/or data),on a tangible medium (such as magnetic or optical domains); and (iii) issubstantially less persistent than permanent storage. Alternatively,data storage may be more persistent and/or permanent than the type ofstorage provided by persistent storage 210.

Storage management program 300 may include both machine readable andperformable instructions and/or substantive data (that is, the type ofdata stored in a database). In this particular embodiment, persistentstorage 210 includes a magnetic hard disk drive. To name some possiblevariations, persistent storage 210 may include a solid state hard drive,a semiconductor storage device, read-only memory (ROM), erasableprogrammable read-only memory (EPROM), flash memory, or any othercomputer-readable storage media that is capable of storing programinstructions or digital information.

The media used by persistent storage 210 may also be removable. Forexample, a removable hard drive may be used for persistent storage 210.Other examples include optical and magnetic disks, thumb drives, andsmart cards that are inserted into a drive for transfer onto anothercomputer-readable storage medium that is also part of persistent storage210.

Communications unit 202, in these examples, provides for communicationswith other data processing systems or devices external to serversub-system 102. In these examples, communications unit 202 includes oneor more network interface cards. Communications unit 202 may providecommunications through the use of either or both physical and wirelesscommunications links. Any software modules discussed herein may bedownloaded to a persistent storage device (such as persistent storagedevice 210) through a communications unit (such as communications unit202).

I/O interface set 206 allows for input and output of data with otherdevices that may be connected locally in data communication with servercomputer 200. For example, I/O interface set 206 provides a connectionto external device set 214. External device set 214 will typicallyinclude devices such as a keyboard, keypad, a touch screen, and/or someother suitable input device. External device set 214 can also includeportable computer-readable storage media such as, for example, thumbdrives, portable optical or magnetic disks, and memory cards. Softwareand data used to practice embodiments of the present invention, forexample, storage management program 300, can be stored on such portablecomputer-readable storage media. In these embodiments, the relevantsoftware may (or may not) be loaded, in whole or in part, ontopersistent storage device 210 via I/O interface set 206. I/O interfaceset 206 also connects in data communication with display device 212.

Display device 212 provides a mechanism to display data to a user andmay be, for example, a computer monitor or a smart phone display screen.

The programs described herein are identified based upon the applicationfor which they are implemented in a specific embodiment of theinvention. However, it should be appreciated that any particular programnomenclature herein is used merely for convenience, and thus theinvention should not be limited to use solely in any specificapplication identified and/or implied by such nomenclature.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

II. Example Embodiment

FIG. 2 shows flowchart 250 depicting a method according to the presentinvention. FIG. 3 shows storage management program 300 for performing atleast some of the method operations of flowchart 250. This method andassociated software will now be discussed, over the course of thefollowing paragraphs, with extensive reference to FIG. 2 (for the methodoperation blocks) and FIG. 3 (for the software blocks).

Processing begins at operation S255, where heatmap module 302 of storagemanagement program 300, collects and maintains (that is “generates”) afirst heatmap (see definition, below). This heatmap reflects accessoperations performed with respect to original data block (also called“original logical block”) 251 previously saved in the fast accessphysical address space 245 of first tier module (“mod”) 241 ofmulti-tier file system device 240 (see FIGS. 1A and 1B). In thisembodiment, first heat map is generated by counting all accessoperations made to data block, regardless of: (i) whether it is readtype, write type or other type of access; (ii) amount of data of theblock that is implicated in the access operation; (iii) time betweensuccessive access operations; (iv) how long in the past the accessoperation occurred; (v) the identity of the program or software makingthe access and/or using the results of the access operation; and/or (vi)time of day/calendar date/scheduling with respect to scheduled backupsand/or defragmentations, etc. Alternatively, in other embodiments, aheatmap may discount certain access and/or types of access, and/ordifferently weight different accesses depending upon the specificcharacteristics of a given access operation.

Processing proceeds to operation S260, where snapshot mod 304 takes asnapshot that includes the first logical block as previously saved inspace 245 of mod 241 of device 240 (see FIG. 1B).

Processing proceeds to operation S265, where revision mod 306 receivesan indication that original logic block 251 (see FIG. 1B) is going to berevised (which means that original logic block 251 will be copied(albeit in a revised form) to a revised logical block). Morespecifically, in this example, original logic block 251 was copied tofast access physical address space 245 of first-tier mod 241 ofmulti-tier file system device 240 after a previous revision to its data.Alternatively, original logical block 251 may have been written to space245 immediately upon its genesis.

Multi-tier file system device 240 is a device that stores datacorresponding to a file system using more than one “tier” of storage. Inthis embodiment, device 240 has two tiers as follows: (i) first-tier mod241, which is a solid state storage device where all of its physicallocations are accessible at substantially the same (very fast speed);and (ii) second-tier mod 242 is a disk based storage device that hasstorage locations in three access speed zones (fast space 246 near outercircumferential edge of disk, slow space 248 near center of disk andmedium space 247 between fata and slow spaces). Compared to first-tiermod 241, second-tier mod 242 provides slower access to saved data, evenin its fastest space 246. Alternatively, some storage systems controlledaccording to embodiments of the present disclosure may have more, orfewer, tiers. Also, as demonstrated by first-tier mod 241, some tiersmay have storage space which is subject to a substantially uniformaccess speed. However, in most, if not all, embodiments of the presentdisclosure, some physical storage locations will experience fasteraccess than others. In this example, original logical block 251 isstored in the fastest accessible space available in device 240. Thisstorage space is relatively desirable, and in some embodiments, ispreferably reserved for data that will be accessed frequently.

In this embodiment, multi-tier file system device 240 is part ofexternal device set 214 of sub-system 102. Alternatively, device 240could be an integrated part of computer 200 (see FIG. 1A). As a furtheralternative, device 240 could be located in client computer sub-systems104, 106 (see FIG. 1A). As yet a further alternative, device 240 couldbe distributed among different physical locations.

Processing proceeds to operation S270, where: (i) heatmap mod 302generates a heatmap of predicted accesses to the logical block after itis revised; (ii) save mod 308 selects a second physical storage locationfor saving the revised logical block based, at least in part, upon theheatmap of predicted accesses; and (iii) save mod 308 saves the revisedversion of original logical block 251 as revised logical block 252.

In this embodiment, the map of predicted accesses (sometimes hereinreferred to as a second heatmap) is identical to the heatmap generatedat operation S255 because it is assumed that future accesses of therevised logical block will be similar to past accesses of the originallogical block. Alternatively, the second heatmap may be based upon thefirst heatmap without being identical to it, for example: (i) recentaccesses may be weighted more heavily than long-ago accesses in thesecond heatmap; (ii) the second heatmap may only count accesses from thefirst heatmap that are made by certain pieces of time-critical,low-latency software; and/or (iii) the second heatmap may consider therate of change access frequency, taken over time, and make an adjustmentto the access count of the operation S255 heatmap based on that.

In this embodiment, the heatmap of operation S255 indicated thatoriginal data block 251 was not being accessed very frequently at all.For this reason, the physical storage location for the revised logicalblock was chosen to be in 248 slow space of relatively slow access tier242 (see FIG. 1B). This slow access will likely be acceptable becauserevised data block 252 will probably not be accessed very often.Alternatively, if the slow space 248 of mod 242 were full, then revisedlogical block 252 might be chosen to be located in medium space 247 ofsecond-tier mod 242 of multi-tier file system device 240.

Some embodiments of the present invention may place the active andinactive logical blocks on faster or slower portions of a storagedevice, based on the heatmap distribution data set, where the storagedevice is any type of storage device that has storage addresses thatperform relatively faster or slower than other storage addresses on thedevice. Physical placement of inactive and active logical blocks isdescribed in further detail below, in section III (Further Comments andEmbodiments) of this detailed description, and with reference to FIG.6).

III. Further Comments and/or Embodiments

In some embodiments of the present invention, inner tracks of a disktype storage device are combined as one storage tier whereas outertracks are combined as another storage tier and the speed differencebetween these two storage tiers becomes a differentiating factor.

The following terminology is used in connection with a file or part of afile, herein called a “data block”: (i) FBi—file block—refers to a datablock wherein FBi holds the address of a logical block corresponding tothe data; (ii) LBnnn—logical block—the data block at a storage systemphysical address; (iii) DataX—the data included within a logical block.

In a conventional multi-tier storage device, when a client programattempts to read from, or write to a data file, the program refers to acorresponding file block. The file block points to a correspondinglogical block where the data is stored.

Consider an illustrative example wherein a snapshot is taken for backuppurposes only, in a conventional copy-on-write (COW) storage system, andthe client program will access only the latest data (also referred to asthe “live data”, or the “primary data”, or the “active data block”).Before the snapshot is taken, the file block (FB0 in this example)points to a logical block (LB100 in this example). LB100 includes DataA,the active data block. LB100 is identified, in this example, as a “hotblock” due to a large number of accesses in the history of DataA.Therefore, LB100 has been placed in outer track(s) of the storagedevice. After the snapshot is taken, and a first post-snapshot writeoperation on FB0 is about to be performed: (i) a new logical block,LB200, is allocated; (ii) a copy of DataA is made; (iii) the copy ofDataA is updated according to the write operation; (iv) the updated copyof DataA is stored as DataB in LB200; (v) FB0 is updated to point toLB200, making DataB the active data block (and making DataA an inactivedata block); (vi) DataB initially shows an access history of zerobecause it has just come into existence and has not yet been accessed;and/or (vii) the conventional multi-tier learning algorithm placesLB200, including DataB, on inner tracks (based on the access history),resulting in a sudden performance degradation.

With regard to the example presented in the paragraph above, someembodiments of the present invention recognize the following facts,potential problems and/or potential areas for improvement with respectto the conventional multi-tier storage device after a snapshot is takenand a first post-snapshot operation to write to FB0 is about to beprocessed: (i) LB100 becomes inactive; (ii) LB100 remains in outer disktracks (due to its identity as a “hot block”); (iii) LB100 is no longerrequired by any user application and unnecessarily takes up outer disktrack space that could be used more advantageously for other data(including LB200), resulting in under-utilization of outer disk trackspace; (iv) initially having no access history, LB200 is not identifiedas a “hot” block and is therefore placed on inner disk tracks; (v) afterthe snapshot, a user program continues to access FB0, which now pointsto LB200; (vi) LB200, not yet having been accessed sufficiently to beidentified as a “hot” block, will stay in the inner disk tracks; and/or(vii) after taking of the snapshot and a first post-snapshot writeoperation against FB0, user program performance, relative to FB0, issuddenly degraded which may further result in unexpected consequences inthe user program behavior. The foregoing example applies when a snapshotis taken for backup purposes only, and the user program accesses onlythe live data.

During a first write after snapshot, when a new logical block isassigned to a given application block, some embodiments of the presentinvention may include one, or more, of the following features,characteristics and/or advantages: (i) provides efficient management ofhigh performance tiers in multi-tier architecture; (ii) transfersheatmap (sometimes referred to herein as “access history”) informationfrom an existing logical block to a new logical block; (iii) based onapplication behavior, predicts whether data is going to be accessed from(a) a snapshot copy (inactive data), (b) from the live data (activedata), and/or (c) distributing access history between the snapshot copyand the live data.

With respect to item (iii) in the paragraph above, the amount of heatinformation to be transferred can be: (i) completely transferred,wherein the snapshot is created exclusively for backup purposes, userapplication programs do not require access to snapshot data, and userprograms access data only from the latest data; (ii) none transferred,wherein user applications access only snapshot data and the latest datais not required (for example, backup applications such as conventionalnetwork data management protocol (NDMP) or cloud gateways, disasterrecovery applications, analytic tools etc.) or (iii) partially, whereinboth snapshot data and latest data (latest blocks) are equallyimportant.

In some embodiments of the present invention, for a given tuple[OldBlock (inactive data), NewBlock (latest data)], a file systeminforms a multi-tier environment with heatmap transfer percentages,during block flush operation. A multi-tier monitoring daemon: (i)updates its monitoring statistics for the OldBlock and the NewBlockbased on the percentages of heat transfer value; and/or (ii) based onthe monitoring statistics, decides whether to place block chunks(logical blocks) on the outer disk tracks or the inner disk tracks.

In some embodiments of the present invention, during snapshot creation,based on the purpose of the snapshot, system administration creates avalue that represents an estimated distribution of application accessesto the snapshot data (inactive data) versus accesses to the live data(latest data). The value “snapAccessPattern” is passed as input to thesnapshot create command, as will be explained in greater detail below.The estimated distribution value is stored in file system snapshotmetadata information tables, for example in a Snapshot Percentage Table(see Snapshot Percentage Table below). The value of snapAccessPattern isreferenced during a first write operation after a snapshot is created,that is, when a new logical block is allocated.

In some embodiments of the present invention, after creation of asnapshot, a first operation to write new data to a file block FB0 withnew data (DataB) results in: (i) allocation of a new logical block,LB200; (ii) the old data (DataA) remains in the old logical block,LB100; and/or (iii) new data (DataB) goes into LB200.

As shown in table 400 of FIG. 4, case 3 (row 404), accesses byapplication programs are unevenly split between blocks LB100 and LB200.Before a first write (to LB200) after snapshot (see row 402), LB100 hadan access count value of 10,000. In case 3 (row 404), it is predictedthat user programs will access LB100 and LB200 with a 40%-60%distribution (that is, 40% of future accesses will be against LB100 and60% will be against LB200). Some embodiments of the present inventiontransfer heatmap information based on the 40%-60% distribution. Examplesof programs that use snapshot data include: (i) backup applications (asthe data is consistent (not subject to modification) as opposed to livedata, and the backup can be configured to recur at shorter or longerintervals based on the criticality of data); and/or (ii) disasterrecovery tools, which replicate consistent (snapshot) data from aprimary site to a remote site and the replication rate is configuredwith lowest recovery time objective (RTO) and recovery point objective(RPO) (that is the snapshot data is accessed more frequently in order tocomply with the RPO).

After taking of the snapshot, multi-tier monitoring module is informedto reduce the recorded number of accesses for LB100 (the snapshot copy),to 4000 (40%) and the remaining access count of 6000 (60%) istransferred to LB200. Based on a multi-tier heat threshold value, themulti-tier relocation module can determine placement of these blocks(LB100, LB200) as to whether they will be stored on inner or outer disktracks. By this method, a user program will experience no significantchange in I/O latency and/or performance after taking of a snapshot.

In some embodiments of the present invention, communication between thefile system and a multi-tier device is implemented in at least one ofthe following manners: (i) by use of a separate out-of-band protocol;and/or (ii) by use of reserved fields in the write small computer systeminterface command descriptor block (SCSI CDB). Some conventional systemsimplement a mechanism to communicate the heatmap from one storage systemto another, to ensure that in a failover to a remote copy, the correctdata will be stored in outer disk tracks. In contrast, the communicationmechanism, in some embodiments of the present invention, is used forcommunication of percentage heat transfer value from application to themulti-tier device.

In some embodiments of the present invention, copy-on-write operation isperformed at the granularity of the file system block size. A multi-tierstorage device monitors heatmap information at the extent level whichcan consist of multiple file system block size. Enterprise applicationsmodify files according to their requirements which may involve modifyingmultiple file system blocks at the same time. For example, a databasetype application modifies data at the granularity of a user record. Ifthe file system block size is 16 megabytes (MB) and a user record is 128MB, a single user record modification by the database applicationresults in modifying 8 blocks at the file system level. In someembodiments of the present invention, the heat transfer mechanism ishighly efficient when the application access size is comparable with themulti-tier extent size.

Some embodiments of the present invention perform the followingoperations, not necessarily in the order presented: (i) maintainingsnapshot percentage information at file system; (ii) deciding percentageof distribution during snapshot creation; (iii) passing percentageinformation to the multi-tier algorithm/mechanism; and/or (iv) handlingpercentage information at multi-tier. The aforementioned operations willnow be explained in greater detail in the following paragraphs.

Maintaining snapshot percentage information at file system:

As shown in Snapshot Percentage Table below, snapshot percentageinformation is maintained by the file system as snapshot metadata. Insome conventional systems, snapshot metadata includes (i) a snapshotname (column: SnapshotName) for each active snapshot; (ii) timestampinformation about each active snapshot (column: SnapCreateTime); and/or(iii) other fields (not separately shown in the table). In someembodiments of the present invention, a new column (column: OldPercentage Value) is added to Snapshot Percentage Table to store “oldpercentage value” which contains access percentage information (alsocalled snapAccessPattern) in terms of how many blocks are accessed froman old (inactive) version versus latest (active) version of the data.

SNAPSHOT PERCENTAGE TABLE Old Percentage Value SnapshotNameSnapCreateTime (snapAccessPattern) Snap1 12 Aug. 2013 00:00:00 50 Snap213 Aug. 2013 06:30:00 100 Snap3 14 Aug. 2013 06:30:00 60

Deciding percentage of distribution during snapshot creation:

To determine how to distribute the old percentage value between an “old”logical block (inactive version) and a “new” logical block (activeversion), the following mechanism is used in some embodiments of thepresent invention.

In some conventional systems, a file system snapshot is created using acommand line interface with a command such as:

# createSnapshotFS--snapName SnapshotName

System administration, either manually and/or through automated scripts,invokes createSnapshotFS to create a snapshot of the given name. Asnapshot can be created for various purposes including checkpointing andcloning/replication.

In checkpointing, a read-only “moment-in-time” snapshot of a file systemis created, such that the file system can later be restored to the stateit had at the moment the snapshot was created. In checkpointing cases,user programs access data from latest data and not from an earlierversion (inactive data). An example of a command to create acheckpointing snapshot follows:

# createSnapshotFS--snapName “checkpointSnapl”//snapshot created forcheck-pointing purpose In cloning/replication, a moment-in-time image ofthe file system is created and data from that image is copied to anotherlocation (such as a remote storage device). In cloning/replicationcases, user programs access data from the snapshot copy and not from thelatest version. An example of a command to create a cloning/replicationsnapshot follows:

 # createSnapshotFS --snapName “replicationSnap1” // snapshot createdfor replication purpose

At the time of snapshot creation, system administration knows thepurpose of creating the snapshot, whether it is for checkpointing,replication, or some other usage. Therefore, it is possible for systemadministration to determine whether a user program is going to accessdata from snapshot copy, the latest version, or both. Some embodimentsof the present invention modify the createSnapshotFS command to get thisinformation from the administration.

Some embodiments of the present invention modify operation of someconventional systems as described above by introducing a new argumentsuch as “snapAccessPattern” to specify “SnapAccess%”. “SnapAccess%”indicates percentages of data a user program is going to access inactivedata compared to accesses of active data. Two examples below showcommands, used in some embodiments of the present invention, to create asnapshot for checkpointing and a snapshot for cloning/replication:

 # createSnapshotFS --snapName “checkpointSnap1” -- snapAccessPattern“0” // No data access from inactive version  # createSnapshotFS--snapName “replicationSnap1” -- snapAccessPattern “100” // Data accessonly from inactive version

In some embodiments, if user programs are predicted to access data fromboth inactive and active data, administration can determine a usagepattern, based on past access behavior, and assign a SnapAccess value.For example, if administration determines 40% of overall access will befrom the inactive data and the remaining 60% are from live data, thefollowing example command is issued:

 # createSnapshotFS --snapName mixedUsageSnap1 -- snapAccessPattern “40”// 40 % Data access from inactive version and remaining from activeversion.

The file system internally updates the “Old Percentage Value” entry fora given snapshot (see the column “Old Percentage Value” in SnapshotPercentage Table above), and uses this value during copy-on-write forheatmap transfer.

Passing percentage information to the multi-tier algorithm/mechanism isshown in flowchart 500 of FIG. 5, which includes the followingoperations (with process flow among and between the operations as shownby arrows in FIG. 5): S502, S504, S506, S508, S510, S512, S514, S516 andS518.

As shown in flowchart 600 of FIG. 6, percentage information atmulti-tier is handled, in some embodiments of the present invention, asfollows:

Get <LB-old, LB-new, Old-Percentage-Value>from the file system(operation S602).

“HeatMapCountCurrent” is assigned as the heatmap count for LB-old from amulti-tier monitoring table (not separately shown in the Figures)(operation S604).

If Old Percentage value is 0 (decision S606, “Yes” Branch), in themulti-tier monitoring table, assign HeatMapCountCurrent as heatmap countfor LB-new and reset heatmap count for LB-old (operation S608). EvictLB-old from OUTER disk tracks (operation S610).

If the old percentage value is not 0 (decision S606, “No” Branch), thefollowing operations are performed:

 (S612): HeatMapCountOld = HeatMapCountCurrent × OldPercentageValue /100  (S614): HeatMapCountNew = HeatMapCountCurrent − HeatMapCountOld

(S616): In multi-tier monitoring table assign HeatMapCountOld for theinactive data block (LB-old) and assign HeatMapCountNew for the activedata block (LB-new).

Although the present disclosure discusses cases when multi-tiermonitoring is done at the file system block level, in general similarimplementations can be done at other file system levels, including atthe file level, at database record level, at the storage medium sectorlevel, etc.

Some embodiments of the present invention may include one, or more, ofthe following features, characteristics and/or advantages: (i) keepstrack of outer vs. inner partition for erasure coded/fixed layout; (ii)based on application behavior, determines whether data is going to beaccessed from snapshot (inactive data) or from the latest data (activedata), based on which heatmap is calculated; and/or (iii) transfers theheatmap to the logical snapshot chunks during first write.

Some embodiments of the present invention may include one, or more, ofthe following features, characteristics and/or advantages: (i) solves aphysical issue on disk storage device, that is, the storage deviceperforms better on the outer zone of a disk platter than on the innerzone; (ii) detects different input/output (I/O) scenario issues toimprove the performance of a taken snapshot; (iii) provides efficientmanagement of high performance tiers in multi-tier architecture suchthat during first write after snapshot, when a new logical block isassigned to given application block; (iv) transfers heatmap informationfrom an existing logical block to a new logical block; (v) based onapplication behavior (whether data is going to be accessed from snapshotcopy or latest data) decides how much of the heatmap information istransferred from the old logical block to the new logical block.

The amount of the heatmap information that is transferred can be: (i)100% (when, for example (a) the snapshot is created only for backup, (b)data in the snapshot is not required, and/or (c) applications areconfigured to access data from only the latest data); (ii) 0% (whenapplications access only snapshot (inactive) data and the latest(active) data is not required); or (iii) mixed (any percentage between0% and 100%, in proportion to accesses predicted to be taken frominactive data versus active data, for example 50% when both inactive andactive blocks are predicted to be accessed in equal amounts).

IV. Definitions

Present invention: should not be taken as an absolute indication thatthe subject matter described by the term “present invention” is coveredby either the claims as they are filed, or by the claims that mayeventually issue after patent prosecution; while the term “presentinvention” is used to help the reader to get a general feel for whichdisclosures herein are believed to potentially be new, thisunderstanding, as indicated by use of the term “present invention,” istentative and provisional and subject to change over the course ofpatent prosecution as relevant information is developed and as theclaims are potentially amended.

Embodiment: see definition of “present invention” above—similar cautionsapply to the term “embodiment.”

and/or: inclusive or; for example, A, B “and/or” C means that at leastone of A or B or C is true and applicable.

Including/include/includes: unless otherwise explicitly noted, means“including but not necessarily limited to.”

Module/Sub-Module: any set of hardware, firmware and/or software thatoperatively works to do some kind of function, without regard to whetherthe module is: (i) in a single local proximity; (ii) distributed over awide area; (iii) in a single proximity within a larger piece of softwarecode; (iv) located within a single piece of software code; (v) locatedin a single storage device, memory or medium; (vi) mechanicallyconnected; (vii) electrically connected; and/or (viii) connected in datacommunication.

Computer: any device with significant data processing and/or machinereadable instruction reading capabilities including, but not limited to:desktop computers, mainframe computers, laptop computers,field-programmable gate array (FPGA) based devices, smart phones,personal digital assistants (PDAs), body-mounted or inserted computers,embedded device style computers, application-specific integrated circuit(ASIC) based devices.

User/subscriber: includes, but is not necessarily limited to, thefollowing: (i) a single individual human; (ii) an artificialintelligence entity with sufficient intelligence to act as a user orsubscriber; and/or (iii) a group of related users or subscribers.

Logical block: a subset of digital bits that make up a file. A file mayconsist of one or more logical blocks. In a storage device such as ahard drive, a logical block is mapped to a physical address on thestorage device.

Heatmap: a record of access history (and/or predicted future accesses)of a logical block (see definition above), potentially includinginformation such as: (i) frequency of access by application programsthat access the block; (ii) mean time between access events; (iii) whichapplication programs access the block; (iv) proportion of reads versuswrites for each application program that accesses the block; and/or (v)other aspects that are meaningful in embodiments of the presentinvention.

What is claimed is:
 1. A computer-implemented method comprising: savingan original logical block in a file system at a first physical location;generating a first heatmap reflecting access operations on the originallogical block; taking of a first snapshot with respect to at least aportion of the file system including the original logical block;receiving information that the original logical block is going to berevised into a revised logical block; generating a second heatmapreflecting predicted access operations on the revised logical block,with the second heatmap being based at least in part on the firstheatmap; selecting a second physical storage location for the revisedlogical block based at least in part on the second heatmap; and savingthe revised logical block at the second physical storage location. 2.The computer-implemented method of claim 1 wherein the second heatmap isidentical to the first heatmap at the time of the selection of thesecond physical storage location.
 3. The computer-implemented method ofclaim 1 wherein the original logical block and revised logical block areincluded in a file system operating as a “copy on write” type filesystem.
 4. The computer-implemented method of claim 1 wherein: therevised logical block is based at least in part on the original logicalblock; the original logical block is maintained as a snapshot record;and an operation to write to a file, after a snapshot is taken, includesan operation to write to the revised logical block.
 5. Thecomputer-implemented method of claim 1 wherein: the file system includesstorage tiers where access is relatively slower at some tiers andrelatively faster at other tiers; and the selection of the secondphysical storage location is based at least in part upon the relativespeed of a tier corresponding to the second physical storage location.6. The computer-implemented method of claim 1 wherein the revisedlogical block is created responsive to a first requested write operationto a file after a snapshot is taken.
 7. The computer-implemented methodof claim 1 wherein the receipt of information that the original logicalblock is going to be revised corresponds to an earliest in time revisionafter the taking of a snapshot.
 8. A computer program productcomprising: a computer readable storage medium; and computer code storedon the computer readable storage medium, the computer code includingdata and instructions for causing a processor(s) set to perform at leastthe following operations: saving an original logical block in a filesystem at a first physical location; generating a first heatmapreflecting access operations on the original logical block; taking afirst snapshot with respect to at least a portion of the file systemincluding the original logical block; receiving information that theoriginal logical block is going to be revised into a revised logicalblock; generating a second heatmap reflecting predicted accessoperations on the revised logical block, with the second heatmap beingbased at least in part on the first heatmap; selecting a second physicalstorage location for the revised logical block based at least in part onthe second heatmap; and saving the revised logical block at the secondphysical storage location.
 9. The computer program product of claim 8wherein the second heatmap is identical to the first heatmap at the timeof the selection of the second physical storage location.
 10. Thecomputer program product of claim 8 wherein the original logical blockand revised logical block are included in a file system operating as a“copy on write” type file system.
 11. The computer program product ofclaim 8 wherein: the revised logical block is based at least in part onthe original logical block; the original logical block is maintained asa snapshot record; and an operation to write to a file, after a snapshotis taken, includes an operation to write to the revised logical block.12. The computer program product of claim 8 wherein: the file systemincludes storage tiers where access is relatively slower at some tiersand relatively faster at other tiers; and the selection of the secondphysical storage location is based at least in part upon the relativespeed of a tier corresponding to the second physical storage location.13. The computer program product of claim 8 wherein the revised logicalblock is created responsive to a first requested write operation to afile after a snapshot is taken.
 14. The computer program product ofclaim 8 wherein the receipt of information that the original logicalblock is going to be revised corresponds to an earliest in time revisionafter the taking of a snapshot.
 15. A computer system comprising: aprocessor(s) set; a computer readable storage medium; and computer codestored on the computer readable storage medium, the computer codeincluding data and instructions for causing the processor(s) set toperform at least the following operations: saving an original logicalblock in a file system at a first physical location; generating a firstheatmap reflecting access operations on the original logical block;taking a first snapshot with respect to at least a portion of the filesystem including the original logical block; receiving information thatthe original logical block is going to be revised into a revised logicalblock; generating a second heatmap reflecting predicted accessoperations on the revised logical block, with the second heatmap beingbased at least in part on the first heatmap; selecting a second physicalstorage location for the revised logical block based at least in part onthe second heatmap; and saving the revised logical block at the secondphysical storage location.
 16. The computer system of claim 15 whereinthe second heatmap is identical to the first heatmap at the time of theselection of the second physical storage location.
 17. The computersystem of claim 15 wherein the original logical block and revisedlogical block are included in a file system operating as a “copy onwrite” type file system.
 18. The computer system of claim 15 wherein:the revised logical block is based at least in part on the originallogical block; the original logical block is maintained as a snapshotrecord; and an operation to write to a file, after a snapshot is taken,includes an operation to write to the revised logical block.
 19. Thecomputer system of claim 15 wherein: the file system includes storagetiers where access is relatively slower at some tiers and relativelyfaster at other tiers; and the selection of the second physical storagelocation is based at least in part upon the relative speed of a tiercorresponding to the second physical storage location.
 20. The computersystem of claim 15 wherein: the revised logical block is createdresponsive to a first requested write operation to a file after asnapshot is taken; and the receipt of information that the originallogical block is going to be revised corresponds to an earliest in timerevision after the taking of a snapshot.